Al. Melott et al., DEMONSTRATING DISCRETENESS AND COLLISION ERROR IN COSMOLOGICAL N-BODYSIMULATIONS OF DARK-MATTER GRAVITATIONAL CLUSTERING, The Astrophysical journal, 479(2), 1997, pp. 79-83
Two-body scattering and other discreteness effects are unimportant in
cosmological gravitational clustering in most scenarios since the dark
matter has a small particle mass. The collective field should determi
ne evolution; two-body scattering in simulations violates the Poisson-
Vlasov equations. We test this result in PM, (PM)-M-3, Tree, and NGPM
codes, noting that a collisionless code will preserve the one-dimensio
nal character of plane-wave collapse, We find collisionality vanishing
as the softening parameter approaches the mean interparticle separati
on, Solutions for the problem are suggested, involving greater compute
r power, PM-based nested grid codes, and a more conservative approach
to resolution claims.